Re: LM1875 on a single supply

<mrdarrett@[EMAIL PROTECTED]
> wrote in message 
news:a1662fad-e0d7-4306-9e20-195abb1e7311@[EMAIL PROTECTED]
>I was reading the datasheet for the LM1875
> http://www.national.com/ds.cgi/LM/LM1875.pdf
>
> and I noticed that they do have a schematic for a single supply (as
> opposed to a +/- supply).
>
> If running on a single supply, does the chip amplifer consume
> significant power during quiet tracks?
>
> Would this be pretty much the same as running the amplifier in Class A
> mode (vs. Class AB)?
>
> I'm trying to figure out if I really need a +/- power supply, or if I
> can just go with a single supply (easier to build).
>
> Thanks,
>
> Michael

Since the LM1875 is inexpensive, you might try using two of them on a 
single supply, and putting the speaker between the outputs. You would have

to make one amp inverting and the other non-inverting, but you will get 
twice the output voltage and save the capacitors. A single 24 volt supply 
will then give +/- 24 volts, or about 17 VRMS, to an 8 ohm speaker, or 36 
watts. There are lots of 24 VDC supplies available. The downside of this 
approach is making sure the DC level of both amps are equal and about 1/2 
the supply.

If you check SemiElectric's eBay store you will find PC boards and kits
for 
the LM3875, as well as other single and dual amplifier ICs:

http://search.stores.ebay.com/semielectric_audio-amp_W0QQfciZQ2d1QQfclZ3QQfsnZsemielectricQQfsooZ2QQfsopZ3QQfsubZ0QQsaselZ650588702QQsofpZ0

His LM3875s are about $6.50 each. They are larger (56 watts vs 20 watts), 
but seem to be otherwise quite similar. Most of the additional IC pins are

NCs, for heat sinking and mechanical mounting, I suppose. They are only 
$5.90 each from DigiKey, and the LM1875 is $3.28. Wow: 10 to 15 cents per 
watt!

Paul